Okay, so example:
A group of PCs find themselves in the middle of an area completely filled with difficult terrain due to poor life choices. There's a door labeled "Exit from Difficult Terrain" on one end of the room. They're in encounter mode because...I don't know, they're fighting something as well, I don't know. Anyway, one of the PCs decides to go straight for the exit and Strides three times for his turn. Here's the question: How many feet closer do they make it to the door?
I ask this because it's really deceptive. For every square you want to move it takes 10 feet of your Speed. So for your first Stride you move forward two squares (20 feet of movement) then (assuming a Speed of 25) stop because you don't have another 10 feet of movement. You then Stride again, doing the exact same thing, meaning you've moved only 20 feet rather than the 25 that you would expect.
I don't know about you guys, but I find this very awkward because it would mean that a dwarf in difficult terrain and a human in difficult terrain move at the exact same speed. I feel like there should be a caveat about Striding in succession allowing you to move 50 feet once rather than "25" feet twice.
You're free to house rule and perhaps should in this instance that the total movement is halved rather than halving each individual stride action.
But technically, you halve each stride (as far as i know) so yes, you only move 20ft per move action if you have a speed of 25ft. Increments of 10ft move speed work fine, increments of 5ft move speed end up with his weird problem.
As long as each Stride is made in succession without being interrupted by another action (say, a Strike), I see no reason not to simply combine the movement from both Strides into a single pool and calculate movement costs in one go. The division of separate "actions" is an artificial one for gameplay purposes, and adhering to them too closely clearly generates nonsensical results like this:
a dwarf in difficult terrain and a human in difficult terrain move at the exact same speed.
It may not be exactly rules as written, but I am firmly of the opinion that anytime a literal reading of the rules leads to illogical conclusions, said reading needs to be relaxed.